Defer layer rendering to avoid stalls

Bug #7326824

When a layer is taken out of the cache and initialized it gets cleared
to prepare it for future rendering. This triggers the following sequence
of operations:

glBindFramebuffer(layer.fbo)
attach texture storage to FBO
glClear()
glBindFramebuffer(defaultFbo)

The clear forces a resolve on tilers which stalls the CPU for a little
while, thus producing jank during animations. This change moves the
clear to the next frame when we know we will have to execute a resolve
anyway.

Change-Id: Ic1939c25df20ed65a4c48dc81ee549b2cd8b6ec3